Mg—Al—Ca alloys have been developed mainly for die-casting materials. In addition, a hard compound is formed by addition of an excessive amount of Al and Ca which are solute elements, resulting in being brittle, and thus excellent mechanical properties cannot be obtained.
Accordingly, although a magnesium alloy in a low addition amount of Al, Ca has been developed, the strength has not yet been improved. In view of the above facts, as to studies of the Mg—Al—Ca alloy, studies of phase to be formed and studies limited to Mg—Al—Ca alloys in an extremely low addition amount of Al, Ca have been carried out.
Furthermore, in order to make the magnesium alloy practical, it is necessary to enhance incombustibility and to raise its ignition temperature. However, since when improving the incombustibility, there are many cases of lowering the mechanical properties, and the incombustibility and the mechanical properties is in a tradeoff relationship, it is difficult to enhance both of the properties.